The present invention relates to a membrane keyboard assembly, and more particularly to a membrane keyboard having connectors to a processing circuit whereby the desired functions of the membrane keyboard can be identified to the processing circuit.
In the control circuit of a device such as a microwave oven or a computer terminal, a pressure sensitive membrane switchboard or keyboard is frequently utilized to transfer the functions desired by the operator to a microprocessor control circuit. By pressing the desired indicia bearing area of the membrane keyboard, appropriate switching occurs and the microprocessor in turn instructs the device being controlled to perform the desired function. In such devices such as microwave ovens and computers, the microprocessor control circuit is a relatively expensive and difficult to design assembly. Once a proven assembly is designed and accepted by customers for its reliability, it is not desirable to change such a design. However, for various models of the devices being controlled, such as microwave ovens, it is desirable to have an increasing number of controllable functions indicated by the indicia on the membrane keyboard for different models of the products. Accordingly, it is desirable to be able to use this same microprocessor control circuit for the various models of the product, even though these models will have different membrane keyboard assemblies allowing for increased or differing numbers of controllable functions.
One known method of identifying the particular type of indicia bearing membrane keyboard being connected to the particular microprocessor control circuit is to utilize a dual in line digital control switch in the control circuitry. Such switch includes a plurality of digital switches each of which can be thrown in a positive or negative connection configuration thereby providing a coding signal to the control circuitry. Each type of membrane keyboard to be connected to the control circuitry can be identified by a particular code, and thereby the one particular control circuit can accommodate a number of membrane keyboards. This method is not desirable from a cost point of view as such digital switches add a considerable cost to the control circuitry. Further, if one of the switches was incorrectly thrown, upon the assembly of the device or in the use of the device, incorrect control of the device by the membrane keyboard would result.
Another known method of identifying the type of membrane keyboard being connected to the control circuit is to hard wire jumpers usually comprising resistors at particular locations on the control circuit board. The control circuit board is so designed so as to be able to identify the type of membrane keyboard being connected thereto by the coded connection of such jumper elements. Such connections to the control circuit board are undesirable as they usually require separate elements to be connected to the circuit board which, as mentioned above, is desired to be a fully functional and reliable circuit assembly without any changes.
Accordingly, it is an object of the present invention to provide a membrane keyboard having identifying connectors whereby the processing circuit to which it is connected can be told the type of membrane keyboard being so connected.